Multiple line rotating polygon

ABSTRACT

An optical scanning device is provided for producing a multiple line scan. A rotating refractive scanning prism in the form of a polygonal solid having an even number of revolving opposite parallel faces provides a multiple line scan, the lines being separated because the plane parallel pairs of revolving opposite faces are at a small angle to the rotating axis of the prism, which rotating axis is generally perpendicular to the optical axis. The number of lines scanned in such an arrangement is equal to the number of revolving faces on the polygon, and can be increased, in another embodiment of the invention, by providing a plurality of detectors in an array to produce a line raster having a number of lines equal to the number of detectors times the number of revolving sides of the polygon.

Umtedl l 55 Yoder MULTIPLE LINE KUlAllnu run-UV. {75] Inventor: John R.Yoder, Westport, Conn.

{73] Assignee: Barnes Engineering Company,

Stamford, Conn.

[22] Filed: Oct. 27,1971

[2]] Appl, No.: 192,814

Thomas 250/236 c [ll] [451 July 17, 1973 [57] ABSTRACT An opticalscanning device is provided for producing a multiple line scant Arotating refractive scanning prism in the form ofa polygonal solidhaving an even number of revolving opposite parallel faces provides amultiple line scan, the lines being separated because the plane parallelpairs of revolving opposite faces are at a small angle to the rotatingaxis of the prism, which rotating axis is generally perpendicular to theoptical axis. The number of lines scanned in such an arrangement isequal to the number of revolving faces on the polygon. and can beincreased, in another embodiment ofthe invention, by providing aplurality of detectors in an array to produce a line rasterhaving anumber of lines equal to the number of detectors times the number ofrevolving sides of the polygon.

2 Claims, 2 Drawing Figures PAIENIEU I 3. 746.421

IN V ENTOR. JOHN R. YODEI? MULTIPLE LINE ROTATING POLYGON BACKGROUND OFTHE INVENTION Refractive scanning prisms have been utilized in the priorart for high-speed scanning applications such as photography, filmediting, aerial reconnaisance, and many others where it is desirable todetermine the amount of electromagnetic radiation in a given field ofview in a very short period of time. One such scanner is shown in US.Pat. No. 3,253,498 entitled Scanning Mechanism for Electro-MagneticRadiation." The scanning mechanism utilizes a rotating refractive prismfor scanning a line in a field of view and applying incoming radiationonto a detector which is sensitive thereto. In order to obtain amultiple line raster or rectangular scan pattern, other means must beutilized, for example, an auxiliary nutating mirror in the collectingoptics, which requires auxiliary elements in the form of the nutatingmirror as well as additional elements for driving the mirror scan andthe synchronizing of the two scans in order to form a proper raster.Another method cited in the aforesaid patent is to progressively tiltthe rotating axis of the prism as it rotates, which again requiresadditional elements for providing such tilt and synchronizing it withthe rotation rate.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an optical scanning device for producing a multipleline scan in the absence of auxiliary devices.

A further object of this invention is to provide an improved opticalscanning device in which a rotating refractive prism is moved in onlyone direction with respect to the optical axis of the system.

Another object of this invention is to provide an improved opticalscanning device for providing a multiline raster-type scan where thenumber of lines scanned depends on the number of revolving faces of therotating refractive prism and the number of detector elements utilized.

In carrying out these and other objects of this invention in oneillustrative embodiment thereof, a rotating refractive prism in the formof a polygonal solid having an equal number of opposite parallel facesis provided, with each pair of opposite parallel faces of the polygonbeing tilted at a different angle with respect to the axis of rotationof the refractive prism. The number of lines scanned is equal to thenumber of revolving faces on the refractive rotating polygon. In afurther embodi-' ment, the number of lines scanned is increased byincreasing the number of detectors receiving radiation through therotating refracting prism.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an optical schematic diagramof the scanning mechanism embodied in this invention, illustrating onescanning position.

FIG. 2 is an optical schematic diagram of the scanning mechanism shownin FIG. I at a scan position l80 from that of FIG. I, and additionallyillustrates the use of a plurality of detectors in the scanning system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, thebasic elements of the optical scanning device in accordance with thisinvention comprise an optical means 10, a rotating refractive scanningprism 12, and a detector means 25. The optical means 10 is illustratedas an objective lens which images a field of view through the refractiveprism 12 onto the detector 25. It will be apparent that the opticalmeans 10 for collecting the radiation from the field of view may be atotally reflective system, or catoptric, as well as the dioptric systemshown. The rotating refractive prism 12 is in the form of a polygonhaving an equal number of opposite parallel faces. For illustrativepurposes, a four-surface polygon is shown having plane parallel pairs ofopposite faces 14 and I6, and I5 and 17 respectively. The prism 12 isrotated on a shaft 18 driven by motor 20. The material of the prism mustbe capable of passing the electromagnetic radiation which is to bemeasured by the detector means 25. For example, for infrared radiation,silicon or germanium may be utilized. Likewise, the detector means 25must be capa- I ble of responding to the intensity of theelectromagnetic radiation which is to be measured, and further must havea time constant sufi'iciently short to respond to the radiation appliedin accordance with the speed of rotation of the refractive prism 12.

A rectangular raster or scan pattern is provided by the refractive prism12 by tilting the plane parallel pairs of revolving opposite faces 14and 16, and I5 and 17 respectively, so that they remain parallel to eachother, but are at a small angle to the rotating axis of the refractiveprism 12. The axis of rotation of the rpism is orthogonal to the opticalaxis 11 of the optical system. The tilt, or angle on the faces of theprism 12 produce a sidewise displacement of the scanned line from thefield of view. FIG. 1 shows the faces 14 and 16 of the prism 12producing one scan line. When the rotating polygon, or refractive prism12 has moved as shown in FIG. 2, a scan line is produced having an equalsidewise displacement in the opposite direction. It is thus apparentthat each pair of plane parallel surfaces of the scanning prism providesa pair of scanned lines equally displaced from an undeviated scannedline illustrated by the optical axis 11. If several of the face pairs ofthe polygon 12 are tilted by different angles from the rotating axis, agroup of laterally displaced ines is produced. For example, for the foursided scanning polygon 12 as shown in FIG. I, having one surface pair offaces 14 and I6 tilted by one unit and the other pair of surfaces 15 and17 tilted by three units, produces a raster of four evenly spaced lines.The vertical location of the lines would in sequence be +3, +1, 3, 1units from the center of the raster scan. It is apparent that the numberof lines scanned is equal to the number of revolving faces on therefractive prism or polygon 12. The same would hold true for 6, 8, orlarger sized polygons, with the only requirement being that an evennumber of revolving opposite parallel faces be provided, and the angleof tilt bev equally spaced with respect to the number of pairs employed.The equal spacing of the lines provides better resolution of the fieldof view than an unequal spacing of lines of the same field. It should benoted that the rectangular scan pattern or raster is produced withoutthe use of any mechanism other than the rotating refractive prism 12.

Another'way of producing a greater number of lines with the rotatingscanning polygon is by utilizing a multiple detector array. FIG. 2illustrates such an array, with an additional detector means 26. As willbe seen by the dotted lines from the field of view which are imaged onthe detector 26 by the optical means and through the refractive prism12, a different line in the field of view is seen by the detector 26than that seen by detector 25. By thus providing a linear detector arraywith the multifaceted polygon 12, a raster is produced whose number oflines scanned is the number of detector elements times the number ofrevolving sides on the polygon. The provision for the additionalscanning provides better resolution.

The output from the detector means, whether it be a single detector 25or a multiple detector array as illustrated by detectors 25 and 26, maybe processed and applied to a cathode ray tube for presenting a visualimage of the scanned field of view. The tracing of the raster pattern onthe cathode ray tube may be controlled by synchronizing the scanning ofthe cathode ray tube with the rotation of the prism, by providing asynchronizing pickup on the rotating prism from which horizontal andvertical sync pulses are derived and fed to the deflection plates of thecathode ray tube. In a single detector system the scan pattern will bein sequence from one face of the polygon to the next. With a multipledetector array, it will be understood that the scan pattern may beinterlaced with, for example, all the lines from one detector beingtraced, then all the lines from the next, etc., or one line from onedetector, one from the next detector, etc. Although a cathode ray tubedisplay is described, other forms of display or storage may be utilized.

The fact that the present invention requires no auxiliary equipment ordevices for obtaining a multiple line scanned pattern suggests a numberof applications for the system, such as to produce a search oracquisition scan pattern, or to produce a homing or tracking scanpattern. Also, a thermal image of a field of view may be provided with arather coarse resolution, but in combination with a detector array of amodest number of elements to scan a thermal image of a field of viewwith fairly good resolution.

Since other modifications and changes varied to fit particular operatingrequirements and environments will be apparent to those skilled in theart, the invention is not considered limited to the examples chosen forpurposes of disclosure, and covers all changes and modifications whichdo not constitute departures from the true spirit and scope of thisinvention.

I claim:

I. An optical scanning device for producing a multiple line scan in theabsence of auxiliary devices comprising a. a rotating refractive prismhaving a polygonal cross-section orthogonal to the axis of rotation withmultiple pairs of opposite parallel faces,

b. optical focusing means for applying radiation from a field of view tosaid refractive prism,

c. detector means in the focal plane of said optical focusing means forreceiving radiation passed by said refractive prism and developing asignal in response to the intensity of said radiation,

d. means for rotating said refractive prism about an an axis of rotationorthogonal to and intersecting the optical axis of said optical focusingmeans so that multiple pairs of opposite parallel faces of said prismare revolved about said axis of rotation,

e. each pair of opposite parallel faces of said prism being tilted at adifferent angle with said axis of rotation of said refractive prismthereby producing a scan of the field of view in the form of a pluralityof laterally displaced lines, the number of which corresponds to thenumber of revolving opposite parallel faces on said prism.

2. The optical scanning device set forth in claim 1 wherein saiddetector means comprises a plurality of detectors arranged in a lineararray parallel to said axis of rotation whereby the field of view isscanned to produce a number of lines equal to the number of revolvingfaces of said prism times the number of said detectors in said array.

1. An optical scanning device for producing a multiple line scan in theabsence of auxiliary devices comprising a. a rotating refractive prismhaving a polygonal cross-section orthogonal to the axis of rotation withmultiple pairs of opposite parallel faces, b. optical focusing means forapplying radiation from a field of view to said refractive prism, c.detector means in the focal plane of said optical focusing means forreceiving radiation passed by said refractive prism and developing asignal in response to the intensity of said radiation, d. means forrotating said refractive prism about an an axis of rotation orthogonalto and intersecting the optical axis of said optical focusing means sothat multiple pairs of opposite parallel faces of said prism arerevolved about said axis of rotation, e. each pair of opposite parallelfaces of said prism being tilted at a different angle with said axis ofrotation of said refractive prism thereby producing a scan of the fieldof view in the form of a plurality of laterally displaced lines, thenumber of which corresponds to the number of revolving opposite parallelfaces on said prism.
 2. The optical scanning device set forth in claim 1wherein said detector means comprises a plurality of detectors arrangedin a linear array parallel to said axis of rotation whereby the field ofview is scanned to produce a number of lines equal to the number ofrevolving faces of said prism times the number of said detectors in saidarray.